The present invention relates in general to a method and apparatus for conduction of cryogenic liquids, and, in particular, to a cryogenic fluid system having a flexible conduit which enables transfer of cryogenic fluids with minimal leakage.
Several attempts have been made in the past to address the need to efficiently transport cryogenic fluids using a flexible conduit. While these past attempts have provided designs that claim to achieve successful transfer of cryogenic fluids, they have demonstrated certain shortcomings. Most notably, these shortcomings relate to the lack of flexibility of the conduit and the manufacturing costs associated with producing a functional flexible conduit.
Conventional conduits for transporting cryogenic materials are generally constructed from rigid, metallic tubing incorporating costly, welded-in metal bellows which are made of a pleated metal and are ideally capable of one or more of axial, angular, lateral, and torsional movement. While these metal bellows may enable a particular conduit to lengthen/shorten, they traditionally have not however, provided for substantial flexibility (i.e. the ability to bend) throughout the substantial length of the conduit. To the contrary, most conventional cryogenic conduits have merely provided for limited flexibility in discrete locations along the length of the conduit through the use of such above-described metal bellows. While some cryogenic conduits may disclose flexibility throughout the length of the cryogenic conduit, the cost of producing such conduits eliminates the feasibility of their commercial use. Further, such conventional cryogenic conduits having metal bellows often incorporate costly (as well as rigid/inflexible) vacuum jacketing. An exemplary cryogenic conduit that includes vacuum jacketing would be arranged having an inner stainless steel tube through which the cryogenic liquid flows, an outer stainless steel tube that seals a vacuum space forming the xe2x80x9cvacuum jacketxe2x80x9d between the inner and outer tubes, multi-layered insulation between the tubes, and bellows interconnecting adjacent conduit tube sections to accommodate axial extension/contraction and/or flexure of the cryogenic conduit at the section(s) of the conduit which include these bellows.
In addition, adjacent segments of conventional cryogenic conduits generally are attached to one another utilizing one of two time-consuming, inflexible, and costly joint connection options: tube-in-tube connections and welded connections. A tube-in-tube connection is generally a joint device having telescoping male and female components. These tube-in-tube connections generally utilize an in-line seal placed between flanges to inflexibly join adjacent bellow-based cryogenic tubes together. Alternatively, welded connections (generally vacuum insulated) can be made between adjacent pieces of cryogenic conduit. Usually, the welded joint of the adjacent cryogenic conduits is then insulated, and a coupling is moved into place over the welded section, thus immobilizing (i.e. making rigid) that section of the cryogenic conduit.
Accordingly, it would be desirable to develop a cryogenic conduit that exhibits flexibility substantially throughout the length of the cryogenic conduit. Additionally, it would be desirable to develop a method of fabricating a cryogenic conduit that reduces the assembly time and cost of the associated welding and tooling required to assemble the cryogenic conduit.
The present invention is generally directed to a cryogenic fluid system and method of making the same. More specifically, the method and apparatus of the present invention are generally directed to a flexible tube-in-tube-type conduit that is specifically adapted for conducting cryogenic fluid. Herein the term xe2x80x9ccryogenic fluidxe2x80x9d generally refers to a liquid or gas (or combination of liquids and/or gases) that has temperature below (i.e., colder than) about xe2x88x92100xc2x0 F. (Fahrenheit). The cryogenic fluid system of the present invention desirably addresses the lack of conduit flexibility associated with conventional cryogenic fluid systems. Particularly desirable applications of this cryogenic fluid system are in the cooling systems of aircraft/spacecraft flight and/or ground systems. Additional application can be found in using the cryogenic fluid system of the present invention for conduction of cryogenic propellants/fuel and/or fuel components for launch vehicles, aircrafts, spacecrafts, and/or rockets. While various preferred applications of the present invention have been mentioned above, the cryogenic fluid system of the present invention may be utilized in any appropriate application for which conduction of cryogenic fluid is desired/required.
A first aspect of the present invention is embodied in a cryogenic fluid system that has a cryogenic conduit that includes a first tube made of a first composite and having an inner wall and an outer wall. The cryogenic conduit also has a second tube made of a second composite and disposed about the first tube. At least one of these first and second tubes utilizes a silicone rubber-impregnated glass cloth in its construction. A tube liner is disposed against the inner wall of the first tube, and thereby interfaces with a cryogenic fluid that may flow through the first tube. This fluid liner is made from a fluorocarbon polymer. Based upon this construction, the first tube is generally positioned between the second tube and the tube liner. In other words, the tube liner is surrounded by the first tube, which in turn is surrounded by the second tube. Herein, a xe2x80x9ccompositexe2x80x9d refers to a construction that utilizes multiple layers and/or materials, wherein each of these layers and/or materials can be formed of the same, similar, or different substances/compositions.
Various refinements exist of the features noted in relation to the subject first aspect of the present invention as well. Further features may also be incorporated in the subject first aspect of the present invention as well. These refinements and additional features may exist individually or in any combination. For instance, the cryogenic conduit that is associated with the first aspect may be used to fluidly interconnect any appropriate components of a cryogenic fluid system. In one embodiment, a cryogenic fluid source is fluidly interconnected with one end of the cryogenic conduit, while an opposite end of the cryogenic conduit is fluidly interconnected with another component of the cryogenic system (e.g., a rocket engine, cooling jacket, or propellant storage tank). Herein, xe2x80x9cfluidly interconnectedxe2x80x9d refers to a joining of a first component to a second component or to one or more components which may be connected with the second component, or to joining the first component to part of a system that includes the second component so that the molecules of a substance(s) (such as a liquid or gas) may be substantially confined to the system and capable of flowing through the system, including through both the first and second components.
In one embodiment of the first aspect, at least one of and more preferably both of the first composite and the second composite include silicone rubber-impregnated glass cloth as at least a part thereof. At least one of the first and second tubes may utilize a reinforcement cord in its corresponding composite construction. This reinforcement cord generally may be embedded within the first composite of the first tube and/or define at least part of the outer wall of the first tube. Reinforcement cord(s) may additionally or alternatively be embedded within the second composite of the second tube and/or define at least part of the outer wall of the second tube. Put another way, reinforcement cord(s) may be one or both xe2x80x9csandwichedxe2x80x9d between layers of the respective composite material or positioned about the periphery of the first and/or second tube. Generally, each reinforcement cord may be arranged in a helical configuration about a first reference axis; accordingly, both of the first and second tubes may be generally disposed about and extend along this same first reference axis. In other words, the first reference axis may generally span along the entire annular origin of the cryogenic conduit such that any reinforcement cord utilized by the first and/or second tube spirals about the first reference axis along at least a portion of the length of the cryogenic conduit. Usually, any such reinforcement cord is made from reinforcement material such as metal wire, glass fiber-based cable/cord, polyrneric-based cable/cord, and/or any combination thereof. Herein, the term xe2x80x9ccordxe2x80x9d can refer to and is interchangeable with one or more of xe2x80x9cwirexe2x80x9d, xe2x80x9ccablexe2x80x9d, xe2x80x9clinexe2x80x9d, or the like. Moreover, the term xe2x80x9ccordxe2x80x9d includes wrapping a single cord in any of the above-noted manners, as well as wrapping a collection of cords in any of the above-noted manners.
The first tube of the cryogenic fluid system of the first aspect can be designed/configured to have an at least generally annular first layer of silicone rubber-impregnated glass cloth disposed in interfacing relation with the tube liner, a first reinforcement cord wrapped about the first layer, an at least generally annular second layer of silicone rubber-impregnated glass cloth disposed about the first reinforcement cord, and a second reinforcement cord disposed about the second layer. Similarly, the second tube may also be designed/configured to have an at least generally annular first layer of silicone rubber-impregnated glass cloth, a first reinforcement cord wrapped about the first layer, an at least generally annular second layer of silicone rubber-impregnated glass cloth disposed about the first reinforcement cord, and a second reinforcement cord disposed about the second layer. In one embodiment, the first and second tubes each have the above-noted configuration. In either or both instances (i.e., in relation to the first and/or second tube), the corresponding first and second reinforcement cords can be (but do not necessarily have to be) made up of the above-mentioned reinforcement materials.
One embodiment of this first aspect of the present invention generally includes an annulus between the first and second tubes. In other words, the outer wall of the first tube can be spaced from an inner wall of the second tube. Preferably, insulation is generally positioned within the annulus. This insulation preferably includes one or more of cryolite (Na3AlF3), Min-K (e.g., Santocel silica reinforced with asbestos fibre and bonded with organic resin), ceramic fiber-based insulation, and any other appropriate substance that is capable of preventing or at least generally reducing the passage of heat from the first tube to the second tube (or vice versa). In another embodiment, the inner wall of the second tube directly interfaces with the outer wall of the first tube.
As for the tube liner of this first aspect, the fluorocarbon polymer that makes up the tube liner may be generally characterized as a fluoro-ethylene polymer and/or copolymer, and more preferably is a polytetrafluoroethylene or tetrafluoroethylene-hexa-fluoro-propylene copolymer. Such preferred fluoro-ethylene polymers are more commonly known under the trademark of Teflon(copyright) which is manufactured by DuPont of Wilmington, Del. This tube liner may generally have a wall thickness that is within a range of about 0.001 inch to about 0.006 inch, and preferably about 0.003 inch. In one embodiment of this first aspect, the tube liner has a wall thickness of no more than about 0.006 inch.
In one embodiment of the first aspect, a first end of the conduit may be defined by an end of the first tube being joined by a sealant to a corresponding end of the second tube. Another option is to have a first end of the cryogenic conduit defined by an end of the first tube that is co-cured to a corresponding end of the second tube. xe2x80x9cCo-curingxe2x80x9d generally refers to heating the first and second tubes until the respective composites which make up the first and second tubes at least approach their respective curing points so that the first tube can be joined/fused to the second tube via at least generally compressing the two heated tubes together. The first end may also include an additional piece material that overlays one or both the respective ends of the inner and outer tubes to provide support for the first end. One such additional piece of material may be an xe2x80x9cend capxe2x80x9d made of an appropriate material (e.g., silicone rubber-impregnated glass cloth).
Generally, the structural integrity of the cryogenic conduit of this first aspect can be maintained at temperatures of down to about 140 Rankine (xe2x88x92320 degrees Fahrenheit). Further, the structural integrity of the cryogenic conduit of this first aspect can generally be maintained at pressures of up to about 500 pounds per square inch. xe2x80x9cMaintaining structural integrityxe2x80x9d generally means that the cryogenic conduit maintains the ability to transport cryogenic fluid without losing a significant amount of cryogenic fluid from the confines of the cryogenic conduit due to leakage. In one embodiment of the first aspect, the cryogenic conduit may have a maximum leakage rate of about 0.02 SCFM/ft. length/inch diameter. In other words, the cryogenic conduit of the first aspect may leak by no more than about 0.02 standard cubic feet of the cryogenic material per minute per foot length of the conduit per inch inner diameter of the inner conduit aperture. Another embodiment of the first aspect may have a maximum leakage rate of only about 0.01 SCFM/ft. length/inch diameter.
A second aspect of the present invention is embodied by a cryogenic fluid system that has a cryogenic conduit that includes first and second tubes. At least one of these first and second tubes is formed at least in part from silicone rubber-impregnated glass cloth. A tube liner, which is made from a fluorocarbon polymer, is disposed against a first inner wall of the first tube so that the first tube is disposed between the second tube and the tube liner.
Various refinements exist of the features noted in relation to the subject second aspect of the present invention as well. Further features may also be incorporated in the subject second aspect of the present invention. These refinements and additional features may exist individually or in any combination. Generally, each of the various features discussed above in relation to the above-described first aspect of the present invention may be utilized by the second aspect of the present invention as well, alone or in any combination.
A third aspect of the present invention is embodied by a method of making a cryogenic fluid system for conducting cryogenic fluid. The method generally includes forming a first tube on a first mandrel of a first diameter, forming a second tube on a second mandrel of a second diameter, larger than the first diameter, and thereafter sliding the first tube relative to the second tube so as to dispose the first tube within the second tube. That is, the first tube may be slid within the interior of the second tube, or the second tube may be slid about the outer periphery of the inner first tube, so as to position the second tube around the exterior of the first tube. The tube-in-tube arrangement of the first and second tubes may generally be referred to as a cryogenic conduit. The method of this third aspect of the present invention generally includes this cryogenic conduit being integrated into the cryogenic fluid system.
The first tube of the third aspect is generally fabricated by forming a first tubular layer of silicone rubber-impregnated glass cloth about the first mandrel, winding a reinforcement cord about the first mandrel after the first tubular layer is formed, and forming a second tubular layer of silicone rubber-impregnated glass cloth about the first mandrel after the reinforcement cord is wound about the first mandrel. In other words, the first mandrel is surrounded by a preferably substantially uniform cover of material defining the first tubular layer. Then the reinforcement cord is coiled around the first mandrel such that the first tubular layer is at least generally positioned between the reinforcement cord and the first mandrel. This is followed by another preferably substantially uniform cover of material defining the second tubular layer such that the reinforcement cord is sandwiched between the first and second tubular layers. Put another way, the reinforcement cord is embedded between the first and second tubular layers of the silicone rubber-impregnated glass cloth. Heat is then applied at least to the first tubular layer and the second tubular layer thus fusing at least part of at least one of the first and second tubular layers to join the first and second tubular layers to one another. The second tube of the cryogenic conduit is generally formed in the same manner as that of the first tube except that the above-mentioned mandrel of a second diameter larger than the first is used to fabricate the second tube. While a xe2x80x9cmandrelxe2x80x9d should be known to those skilled in the art, in relation to the subject third aspect it generally refers to a bar/rod (generally metal) or other appropriate mount that serves as a core around which conduit precursor material may be wrapped/wound, cast, molded, forged, or otherwise shaped into the resultant conduit.
Various refinements exist of the features noted in relation to the subject third aspect of the present invention as well. Further features may also be incorporated in the subject third aspect of the present invention as well. These refinements and additional features may exist individually or in any combination. For instance, a fluoro-ethylene polymer or copolymer (e.g. Teflon(copyright)) can be positioned about the first mandrel prior to forming the first tubular layer of the first tube (e.g., to provide a liner for the cryogenic conduit, and that will interface with a cryogenic fluid that flows through the cryogenic conduit. In one embodiment, a thickness of the fluoro-ethylene polymer or copolymer is within a range of about 0.001 inch up to about 0.006 inch, and in another embodiment is no more than about 0.006 inch. This fluoro-ethylene polymer or copolymer generally may be adhered to the first tubular layer of silicone rubber-impregnated glass cloth, preferably by heating the first tubular layer of silicone rubber-impregnated glass cloth to join at least part of the first tubular layer to the fluoro-ethylene polymer or copolymer via melt-bonding. In another embodiment, an appropriate insulation may be disposed between the first and second tubes. One way to provide this insulation between the first and second tubes may be to apply the insulation around the first tube before installing the first tube inside the second tube. However, other ways of placing insulation between the first and second tubes may be appropriate.
One embodiment of the third aspect can include wrapping or winding an additional reinforcement cord about the mandrel on which the first and/or second tubes are fabricated, after the xe2x80x9coutermostxe2x80x9d tubular layer of silicone rubber-impregnated glass cord is formed. In other words, the xe2x80x9coutermostxe2x80x9d tubular layer of silicone rubber-impregnated glass cord for the first and/or second tube can be positioned at least generally between the original reinforcement cord and the additional reinforcement cord. This additional reinforcement cord can be included in the structure of the cryogenic conduit to provide additional structural support for the cryogenic conduit. In other words, this additional reinforcement cord can be included in the structure of the cryogenic conduit for supplemental structural support. Further, this additional reinforcement cord can be made from the same or different reinforcement material as the original cord.
It may be desirable in accordance with the third aspect to provide a joint at one or both ends of the cryogenic conduit. In one embodiment, a first end of the cryogenic conduit can be formed by adhesively joining or co-curing an end of the first tube to a corresponding end of the second tube after sliding the first tube into the second tube. This may be accomplished by clearing the insulation (if any is present) from between the respective ends of the first and second tubes so that the outer wall of the first tube can contact the inner wall of the second tube. A sufficient amount of heat and/or adhesive may then be applied to at least the outer wall of the first tube and/or the inner wall of the second tube so that the first tube and the second tube can be compressed together to bond the first and second tubes together to form an end of the cryogenic conduit.